How (Not) To Cut Your Capillary Column

There are numerous ways to cut a capillary column. Restek has several tools to accomplish this job. There are sapphire scribes, ceramic scoring wafers, wafers with a handle, and diamond blade column cutters. There are also some tools manufactured by other companies that will cut a capillary column. The choice is typically personal preference. No matter what you choose, a square clean cut is extremely important for good chromatography.

A ceramic scoring wafer is used by the majority of chromatographers, so that will be the focus of my post. Restek’s version is pictured below. Ceramic scoring wafers are readily available from most all chromatography companies, are inexpensive, and are fairly easy to use.

The flat straight edge of the wafer is used to lightly score the fused silica tubing. After scoring the fused silica, slight pressure from one’s finger will break the tubing. If done properly, a nice clean square cute is obtained. Here are some good Restek resources, that contain pictures and guidance, for properly cutting columns:

Ceramic Scoring Wafer Instruction Sheet

Column Cutting, for making the Optimal Coupling: Do you use your column-Scoring-Wafer the Right Way?

(S)light pressure and lightly tapping to break the fused silica is stressed in any column cutting instruction guide. If too much pressure is used, you’ll get cuts like the ones in the photos below. These poor cuts have shards of fused silica inside the column and fissures on the side of the column. The shards will create active sites in the column and cause all types of issues. The fissures can perpetuate the break downwards and make the column end brittle. The column on the far right is so badly damaged that it appears to have the pressure from a pair of scissors used to make the cut.

 

If you ever do make a poor cut, make a new cut about 8-12 inches from the end. Cracks can run upwards to 6 inches.  This will help ensure that your new (and good) cut removes any shards and the potential for brittleness caused by a fissure.

As a note, over time a ceramic scoring wafer will dull. As the edge dulls, more pressure will be required to break the fused silica. That excessive pressure will first lead to non-square cuts and eventually to the issues pictured above. When all sides of the wafer start to show signs of being dull, discard and replace it. The same holds true with a sapphire scribe. If you prefer the diamond blade cutter, replace the diamond cutting wheel when you observe poor cuts.

I would like to thank Wendy Henninger, one of our QS Engineers, who provided the detailed photos of the poorly cut columns.

 

 

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4 Responses to “How (Not) To Cut Your Capillary Column”

  1. Steven Pruskin says:

    I’ve found the key to getting a good cut is practice. Someone new at it has a hard time, over time they get better and they never know why. Once you get the feel for it, it doesn’t matter what tool you use.

  2. Chas Simons says:

    Hello Steven,

    Thank you for reading Restek’s ChormaBLOGraphy. You are absolutely correct that column cutting takes practice, no matter what tool you use. Keeping an older column on hand for training purposes is not a bad idea.

    Chas

  3. Christian Merchant says:

    Practice does help. I can now sense exactly when the wafer has scored through the polyimide and just started to scratch the fused silica underneath, letting me know I’ve scored enough for a clean cut. I then pull gently on the end to be removed and bend slowly, creating a nice fast break.

    One thing to mention is there’s two sides to each scoring wafer and not everyone knows that! Using the sawtoothed side for glass capillary columns will never produce a clean cut, and the printing on the cutters isn’t always on the same side. I always feel the edges with my finger to make certain I’m using the correct edge.

  4. Chas Simons says:

    Hello Christian,

    Thank you for the comments. The “sawtooth” or serrated edge is used for cutting metal columns, such as Restek’s MXT columns. Some day, that can be an entirely separate blog post. As you mention, the easiest way to determine the straight and/or serrated edge is by feel.

    Chas

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